Rehabilitation of a complex industrial wastewater containing heavy metals and organic solvents using low cost permeable bio-barriers – From lab-scale to pilot-scale

Abstract

This work addresses the treatment of a complex industrial effluent containing high concentrations of metals and spiked with two organic solvents (diethylketone – DEK, and methyl ethyl ketone - MEK) using an eco-friendly approach. The treatment system herein proposed consists of a bio-barrier that combines the adsorption capacity of sepiolite with the properties of a Streptococcus equisimilis biofilm with proven ability in the degradation and bioremoval of a wide range of pollutants.Results from the open-systems experiments conducted with raw sepiolite exposed to a binary mixture of DEK and MEK revealed the preference of the sorbent towards DEK. The results from the biodegradation experiments also revealed the preference of S. equisimilis to degrade/bioremove DEK over MEK independently of their initial concentration (100 mg/L to 3200 mg/L). Bioremoval percentages higher than 95% were reached for all the concentrations of DEK tested. The lab-scale experiments conducted in open-system with sepiolite and sepiolite covered with biofilm, and the pilot-scale experiment conducted in closed-loop, revealed similar performances on the rehabilitation of an industrial effluent containing heavy metals and additionally spiked with DEK and MEK. Regarding the selectivity towards the different pollutants, Cu was preferentially removed over Cr and Ni, and DEK over MEK. The presence of the biofilm allowed an improvement on the removal of heavy metals, particularly Cr, besides preventing the leaching of Al, Fe, and Mg from the sepiolite structure, an extremely important advantage in comparison to the system without biofilm. EDS analyses performed in sepiolite samples revealed the presence of several metals (Cr, Cu and Ni), proving thus the occurrence of sorption processes by sepiolite and by sepiolite covered by biofilm. The breakthrough data obtained in the open-systems were properly described by the Dose Response and the Yoon and Nelson mathematical models. More research work needs to be performed with complex industrial effluents aiming the optimization of the treatment systems to be applied in real context scenarios.